Determining the Influence of a Low-Head Dam on Macroinvertebrate Communities in the Bouie River

The Bouie River is a tributary of the Leaf River and belongs to the Pascagoula River watershed, the latter of which has no flow impediments in the form of sills or dams. The Bouie River has been heavily altered in the lower 10 river kilometers (rkm) from aggregate mining (creating a series of deep gravel pits) and the presence of an earthen and concrete low-head dam (sill) located 6 rkm from the mouth of the river. However, despite these alterations, the immediate stretch of river below the low-head dam is a known spawning habitat for diadromous fish species, including the protected Gulf Sturgeon. The purpose of this study was to determine the impact of the low-head dam on aquatic macroinvertebrates communities in the Bouie River to infer ecosystem health by comparing the abundance of Ephemeroptera, Plecoptera, and Trichoptera above and below the structure. From April to June of 2021, 2022, and 2023, a sequence of drift nets was set in tandem in randomized river reaches on either side of the structure. Net contents were preserved in formalin and all macroinvertebrates were sorted and identified to the lowest taxonomic level possible. Macroinvertebrates from fourteen samples were identified with seven samples from below and seven samples from above. I performed an ANOVA test to examine if there were differences in taxa relative abundance (as catch per unit effort) above and below the low-head dam as well as across multiple years. To determine if differences existed in macroinvertebrate community structure, I used non-metric multidimensional scaling plots. I found no difference in abundance of Ephemeroptera, Plecoptera, and Trichoptera above and below the low-head dam nor any differences in community assemblage. My results suggest the low-head dam has minimal influence on the macroinvertebrates in this stretch of the Bouie River, perhaps related to the taxonomic resolution or because of the modified river channel upstream of my above low-head dam sampling locations. Low-head dams generally alter sedimentation and deposition of detritus above such structures; however, the aggregate mined pits likely act as depositional habitats. My data provides baseline information on the macroinvertebrate communities of this tributary, which may aid in restoration success criteria if the structure is removed and may support conservation measures for species of concern in this region.